Wideband receiver and channel scanning method

ABSTRACT

A wideband receiver ( 10 ) comprises a frequency converter ( 16 ) for converting the frequency of a signal inputted through an antenna ( 12 ) by using a local oscillation signal from a local oscillator ( 18 ); a wideband filter ( 20 ) for receiving the output of the frequency converter ( 16 ) and passing a signal component corresponding to the scanning band including the bands of channels; an A/D converter ( 22 ) for converting the output of the wideband filter ( 20 ) into a digital signal; an FFT operational circuit ( 24 ) for receiving the digital signal and subjecting it to high-speed Fourier transformation; and a control circuit ( 26 ) for detecting the channel in communication in a predetermined scanning band on the basis of the results of operation of the FFT operational circuit. The control circuit ( 26 ) repeats the change of the scanning band by changing the frequency of the local oscillation signal, to detect the channel in communication with an assigned frequency range, i.e., a search frequency range.

This application is a 371 of PCT/JP 98/04489 filed on Oct. 5, 1998.

TECHNICAL FIELD

The present invention relates to a wideband receiver, referred to as aso-called scanner, and more specifically, relates to a wideband receiverand a channel scanning method, which can detect a channel at a higherspeed.

BACKGROUND ART

A wideband receiver which scans a wide frequency band, detects a channelappearing in the frequency band, and according to circumstances,demodulates a signal in the detected channel, and outputs this signal asan acoustic signal has heretofore been known. As shown in FIG. 1, such awide band receiver comprises, in general, an antenna 12, an RF amplifier14, a frequency converter 16, a frequency synthesizer 18 consisting of aPLL (Phase Locked Loop) circuit and a voltage controlled oscillator(VCO), a narrow-band filter 102, a detector 104, a control circuit 106and a demodulation circuit 108.

Radio wave received by the antenna 12 is converted to an intermediatefrequency signal by the frequency converter 16 via the RF amplifier 14.This intermediate frequency signal is provided to the detector 104,through the narrow-band filter 102 substantially having a frequencybandwidth, that is, a step width. The detector 104 detects whether acommunication signal is included or not in the signal having passedthrough the narrow-band filter 102, and outputs a detection signalindicating the detection of the communication signal to the controlcircuit 106. The control circuit 106 responds to, for example, thedetection signal, fixes the frequency of the local oscillation signalfrom the frequency synthesizer 18, controls each circuit so that thedetected communication signal is output to the demodulation circuit 108,or changes the frequency of the local oscillation signal, and controlseach circuit so that an intermediate frequency signal having otherfrequency is output from the frequency converter 16.

In this manner, by repeating a processing in which the frequency of theintermediate frequency signal is changed, and a narrow-band filterhaving a predetermined frequency bandwidth (channel width) filters thissignal, and it is detected whether a communication signal is included ornot in the filtered signal, signals in communication included in thesearch frequency range to be searched are detected, and one of thesesignals can be output in speech or the like.

In the conventional wideband receiver, however, it is required toexecute changes of the frequency of the local oscillation signal by thenumber of channels included in the search frequency range, that is, by(search frequency range/channel width) times. For example, whenaeronautical radio having a search frequency range of from 108 MHz-136MHz, and a frequency bandwidth, i.e., channel width of 25 kHz is to bedetected, it is necessary to change the frequency of the localoscillation signal for (24 M/25 k)=960 times. In general, the frequencycontrol time of a frequency synthesizer, that is, the time until thefrequency is changed and presence of a predetermined signal is detectedis several tens msec. Therefore, iteration of frequency changes andchannel search for many times becomes an obstruction in improving thesearch speed of the receiver.

Moreover, in the conventional wideband receiver, when a certain channelis being detected, it can be only detected whether or not there is asignal in communication in that channel, and the signal in that channelcan only be demodulated and output, and detection of a plurality ofchannels and demodulation and output of a signal at the same time cannotbe performed.

It is an object of the present invention to provide a wideband receiverthat can detect channels in the search frequency range at a high speed,and can regenerate that signal.

It is another object of the present invention to provide a widebandreceiver that can perform detection of a channel and demodulation andoutput of a signal in that channel or in other channels, at the sametime, thereby enabling realization of high-speed search, which is easyto use.

DISCLOSURE OF THE INVENTION

The object of the present invention is achieved by a wideband receiverthat receives radio wave, and uses a frequency range allocated tocertain broadcasting as a search frequency range to detect a channelbeing in communication in that search frequency range, comprising: afrequency converter which converts the frequency of a signal input viaan antenna, by use of a local oscillation signal from a localoscillator; a wideband filter connected to the frequency converter,which receives the output of the frequency converter to allow a signalcomponent corresponding to a scanning band including a bandwidth of atleast a plurality of channels to pass therethrough; an A/D converterconnected to the wideband filter, which receives the signal componentand converting the signal component to a digital signal; an FFTarithmetic circuit connected to the A/D converter, which receives thedigital signal and subjects the signal to a fast Fourier transform; anda detection circuit which detects a channel being in communication in apredetermined scanning band, based on the calculation result by means ofthe FFT arithmetic circuit; wherein it is constructed such that afrequency of a local oscillation signal is changed to change thescanning band, whereby a channel being in communication is detected inan allocated frequency range.

According to the present invention, a signal corresponding to thescanning band including a bandwidth of a plurality of channels is takenout by a wideband filter. This signal is further subjected to the FFToperation to sequentially calculate a power with respect to thefrequency, and a channel being in communication can be detected in thescanning band, by referring to this power. Moreover, according to thepresent invention, a plurality of channels can be detected by scanningof the scanning band. As a result, the number of times of frequencychange of the local oscillation signal and the number of times offrequency transform can be reduced, thereby enabling reduction in theprocessing time required for scanning of channels.

In a preferred aspect of the present invention, the width of a scanningband of a wideband filter is set to be:

I _(bw) /C _(bw) >T _(fft) /T _(ch)+1

(wherein I_(bw) is a scanning band width, C_(bw) is a search frequencyrange, T_(fft) is time for operation in the FFT arithmetic circuit, andT_(ch) is frequency control time of a local oscillator).

In the above aspect, it is more preferable that the left side in theabove expression is sufficiently large.

In the more preferable aspect of the present invention, it is soconstructed that the wideband receiver comprises a demodulation circuitconnected to the A/D converter, which receives a digital signal anddemodulates the signal in the detected channel, so that demodulation ofa signal in a predetermined channel is realized in parallel with theoperation of the FFT arithmetic circuit.

Alternatively, it may be constructed such that the wide band receivercomprises a demodulation circuit connected to the wideband filter, whichreceives the output from the wideband filter to demodulate a signal in apredetermined channel, so that demodulation of a signal in apredetermined channel is realized in parallel with the operation of theFFT arithmetic circuit. According to these aspects, it becomes possibleto realize detection of a channel and demodulation of the detectedchannel in parallel, in a certain scanning band.

According to another aspect of the present invention, a widebandreceiver that receives radio wave, and uses a frequency range allocatedto certain broadcasting as a search frequency range to detect a channelbeing in communication in the search frequency range, comprises: signalextraction means for extracting a signal corresponding to a scanningband corresponding to a search frequency range, or to a scanning bandobtained by dividing the search frequency range into at least two; powercalculation means for receiving a signal extracted by the signalextraction means and calculating a power with respect to the frequency;and channel detection means for detecting a channel being incommunication in the scanning band, based on the calculation result fromthe power calculation means, wherein a channel being in communication isdetected in the search frequency range by changing the scanning bandaccording to need.

In this aspect, it is possible to detect a plurality of channels in thescanning band, and hence the number of times of changing the scanningband can be reduced, thereby enabling reduction in the processing timefor channel scanning.

Moreover, the object of the present invention can be achieved by amethod comprising steps for realizing the above construction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an outline of a conventional widebandreceiver.

FIG. 2 is a block diagram showing an outline of a wideband receiveraccording to an embodiment of the present invention.

FIG. 3 is a flowchart showing an outline of processing executed by awideband receiver according to this embodiment.

FIG. 4 is a diagram for explaining a band of a signal detected by a BPFin a wideband receiver according to this embodiment.

FIGS. 5(a) to 5(c) are diagrams for explaining relation between achannel now being scanned and a channel being demodulated in thisembodiment.

FIG. 6 is a block diagram showing an outline of a wideband receiveraccording to another embodiment of the present invention.

FIG. 7 is a flowchart showing a processing executed by a widebandreceiver according to the other embodiment of the present invention.

DESCRIPTION OF PREFERABLE EMBODIMENTS OF THE INVENTION

Embodiments of the present invention will now be described in detail,with reference to the accompanying drawings. FIG. 2 is a block diagramshowing hardware of a wideband receiver according to a first embodimentof the present invention. Elements the same as those of the conventionalwideband receiver shown in FIG. 1 are denoted by the same numerals. Asshown in FIG. 2, a wideband receiver 10 according to this embodimentcomprises an antenna 12, an RF amplifier 14, a frequency converter 16, afrequency synthesizer 18 consisting of a PLL circuit and a VCO, awideband filter 20 having a predetermined IF band, an A/D converter 22,an FFT arithmetic circuit 24, a control circuit 26 for controlling theseelements, and a demodulation circuit 28.

In this embodiment, the wideband receiver 10 is capable of detectingnarrow FM, commercial FM broadcasting, TV broadcasting or the like.However, in this specification, description will be made, taking anexample of detection of aeronautical radio having a frequency bandwidth(channel width) of 25 kHz.

The wideband filter 20 according to this embodiment comprises a passbandof 300 kHz. That is to say, the wideband filter 20 is constructed so asto have an IF band of 300 kHz.

Moreover, the A/D converter 22 is to convert an input intermediatefrequency signal to digital data at a predetermined sampling frequency(for example, 10 MHz). The FFT arithmetic circuit 24 subjects the inputdigital data to the fast Fourier transform (FFT) operation to calculatea power level of a frequency component in the IF band regarding theinput data. The control circuit 26 controls the operation of the RFamplifier 14 or the demodulation circuit 28, and detects a frequency ofthe signal being in communication, based on the arithmetic results ofthe FFT arithmetic circuit 24.

The processing executed by the receiver 10 constructed as describedabove will be described, with reference to the flowchart in FIG. 3. Forexample, when the power of the receiver 10 is turned on, the A/Dconverter 22 and FFT arithmetic circuit 24 are initialized, and theoscillation frequency of the VCO in the frequency synthesizer 18 is alsoinitialized (step 301).

Then, when a user gives an instruction to search, processing of step 302and after is executed.

In this receiver 10, the radio wave received by the antenna 12 isamplified to a predetermined level by the RF amplifier 14, and providedto the frequency converter 16. A local oscillation signal from the VCOin the frequency synthesizer 18 is provided to the frequency converter16. In this embodiment, by changing the frequency of the localoscillation signal (see step 309 described later), the IF signal outputfrom the frequency converter 16 is filtered by the BPF 20 having arelatively wide band such as 300 kHz, and as shown in FIG. 4, FFToperation is performed for each band of approximately 300 kHz (forexample, numeral 401, 402), to thereby detect a channel included inthese bands.

In step 302, the frequency converter 16 converts the received radio waveto an intermediate frequency signal, based on the local oscillationsignal from the frequency synthesizer 18 (step 302). Then, theintermediate frequency signal is filtered by the BPF 20, and convertedto a digital signal by the A/D converter 22. The FFT arithmetic circuit24 subjects the digital signal output from the A/D converter 22 to theFFT operation (step 303). In the step 303 executed first, the FFToperation is performed with respect to the digital signal correspondingto the band 401 in FIG. 4.

When the FFT operation is completed, the control circuit 26 scans theresults of the FFT operation, to judge whether a channel being incommunication exists or not (step 304). For example, if communication ina certain frequency band (channel) is detected (YES in step 304), thecontrol circuit 26 records necessary information such as the frequencythereof in a memory (not shown), and outputs the information to adisplay unit (not shown) such as a liquid crystal display (step 305).When a user wants to know the communication contents in the frequencyband detected in step 304, the user operates a predetermined switch onthe receiver 10 (YES in step 306). As a result, the demodulation circuit28 is operated and a signal in this frequency band is demodulated, andprovided to an audio output circuit. In this manner, the communicationcontents in the detected channel are output in speech (step 307).

On the other hand, when a predetermined switch is not operated by theuser (NO in step 306), or during output of the communication contents,the control circuit 26 operates again the results of the FFT operation,to thereby judge whether an other channel being in communication existsor not (step 304). Thereafter, when a channel is detected, processing instep 305 to step 307 is repeated.

In this embodiment, while the control circuit 26 confirms the presenceof a channel being in communication by scanning the results of the FFToperation (steps 304 and 305), it is possible to demodulate and outputthe communication contents of a predetermined channel at the same time,by the audio output circuit. This is because the information (frequencyand level) regarding a channel being in communication existing in apredetermined band (in this embodiment, 300 kHz) has been obtained bythe FFT arithmetic circuit 24, and hence while the control circuit 26 isobtaining information regarding a certain channel, the demodulationcircuit 28 can demodulate a signal in other channels and output thesignal to the audio output circuit.

For example, as shown in FIG. 5(a), during reproduction of channel 501,the control circuit 26 can store information regarding a channel 502 ordisplay the information on a display unit. Moreover, unless a userinstructs reproduction of communication contents in channel 502,scanning is advanced, and as shown in FIG. 5(b), the control circuit 26operates to store or display the information regarding channel 503 inthe memory or on the display unit. On the other hand, when output of thecommunication contents in channel 503 is instructed, as shown in FIG.5(c), a signal in channel 503 is provided to the audio output circuitvia the demodulation circuit 28, and the communication contents inchannel 503 is output in speech. Furthermore, regardless of the channelduring demodulation, scanning is advanced sequentially (for example,channel 504).

When scanning in a predetermined scanning band (300 kHz in thisembodiment) is completed (YES in step 308), the control circuit 26instructs the frequency synthesizer 18 to change the oscillationfrequency of the VCO, and in response to this instruction, the frequencysynthesizer 18 changes the oscillation frequency of the VCO, and outputsa local oscillation signal of a new frequency (step 309). For example,when the frequency synthesizer 18 outputs a local oscillation signal, sothat the frequency converter 16 outputs an intermediate frequency signalto detect the band 401 in FIG. 4, then in step 309, the frequencysynthesizer 18 provides a local oscillation signal of a new frequency tothe frequency converter 16, so that the frequency converter 16 outputsan intermediate frequency signal to detect the band 402. In this manner,the frequency of the local oscillation signal is changed through step309, and by repeating steps 302 to 308 again, it becomes possible tosubject each of the bands 401 to 40n to the FFT operation to detect achannel that may be included in each band.

Below is a description regarding comparison of the processing timebetween the receiver 10 according to this embodiment and a conventionalreceiver. Here, it is assumed that the search frequency range isS_(bw)[Hz], the bandwidth of the operation frequency range of anon-search signal, that is, the bandwidth of a channel is C_(bw)[HZ],the frequency control time by means of a local oscillator isT_(ch)[sec], and the operation time by means of the FFT arithmeticcircuit 24 is T_(fft)[sec].

Then, in the conventional receiver, the time T_(sold) for searching thesearch frequency range can be expressed substantially by the followingexpression (1):

T _(sold)=(S _(bw) /C _(bw))×T _(ch)  (1).

On the other hand, in the receiver according to this embodiment, thetime T_(sfft) for searching the search frequency range can be expressedsubstantially by the following expression (2):

T _(sfft)=(S _(bw) /I _(bw))×(T _(ch) +T _(fft))  (2).

Therefore, in, order to make the search time of the receiver accordingto this embodiment smaller than the search time of the conventionalreceiver, the following expression need only be concluded:

T _(sold) >T _(sfft,)

that is,

I _(bw) /C _(bw) >T _(fft) /T _(ch)+1  (3).

In particular, in the expression (3), it is preferable that the leftside is sufficiently larger than the right side.

A more specific comparative example will be described. For example, inJapan, frequency is allocated to the aeronautical radio, a keymachine ofcordless phones and digital car telephones, as shown in Table 1described below.

TABLE 1 Frequency Band Frequency Band Step Aeronautical 108-132 MHz 24MHz 25 kHz radio Cordless 380.2125-381.3125 MHz 1.1 MHz 12.5 kHz phoneKey machine Digital cell- 810.0125-825.9875 MHz 15.975 MHz 12.5 kHz ularphone

As is obvious from Table 1, for the aeronautical radio, channels areallocated in the band of 24 MHz of from 108 MHz to 132 MHz withintervals of 25 kHz. Therefore, the number of channels becomes 24 MHz/25kHz=960. It is considered a case where all the channels are scannedusing the conventional receiver. In the case of the conventionalwideband receiver (for example, the one of a type of changing over thefrequency of PLL as shown in FIG. 1), the time for changing thefrequency and detecting the presence of a channel being in communicationis approximately 20 msec. That is, since the receiver has a speed ofapproximately 20 msec per channel, in order to scan all the channels, itrequires 20 msec×960=19.6 sec.

On the other hand, if the frequency band (scanning band) to be subjectedto the FFT operation is assumed to be 300 kHz, the receiver according tothis embodiment obtains a signal by the number of times of 24 MHz/300kHz=80, and subjects the obtained signal to the FFT operation. Forexample, in a DSP of one generation before the one currently used (in1998), in order to execute the FFT operation having a resolution of 25kHz, being an interval (step) of channels, about 160 μsec will beenough. Therefore, in order to scan all the channels, (20 msec+160μsec)×λ=1.6 sec will be sufficient. 20 msec in the above expression is atime necessary for changing the frequency, corresponding to theconventional wideband receiver.

As described above, according to this embodiment, comparing with thecase where the conventional receiver is used, time of {fraction (1/12)}will be enough in order to scan all the channels.

Similarly, comparison regarding the case where all the channels includedin the frequency band of the cordless phone and the digital cartelephone is shown below, respectively.

1. Cordless Phone Conventional receiver: (1.1 MHz/12.5 kHz)×20 msec=1.76sec. This embodiment: (1.1 MHz/300 kHz)×(500 μsec+20 msec)≠75 msec.

Here, 500 μsec is a time required for performing the FFT operationhaving a resolution of 12.5 kHz by the DSP, and 20 msec in the followingexpression is a time required for changing the frequency of a localoscillation signal.

2. Digital Cellular Phone Conventional receiver: (15.975 MHz/12.5kHz)×20 msec=25.56 sec. This embodiment: (15.975 MHz/300 kHz) ×(500μsec+20 msec)≠1.091 sec.

As described above, in the both cases, it can be seen that the receiveraccording to this embodiment requires a time of approximately 1/23.5 ofthe conventional receiver, as the time required for scanning.

As described above in detail, according to this embodiment, with respectto an intermediate frequency signal, a frequency band containing atleast a plurality of channels is taken out, the signal in the frequencyband is subjected to the FFT operation and a channel included in thefrequency range is detected. Moreover, an optional channel in thenecessary search frequency range can be detected by changing thefrequency band to be taken out. Therefore, it becomes possible to reducethe processing time for detection, by adjusting the frequency bandwidth,and reducing the number of times of changing the frequency band, whichneeds time. Furthermore, if it is in the same frequency band,communication contents in other channels can be reproduced, whiledetecting a channel.

Needless to say, the present invention is not limited to the aboveembodiment, and various modifications are possible within the scope ofthe present invention described in claims, which are included in thescope of the present invention.

For example, in the above embodiment, the demodulation circuit 28 isconstructed so as to receive the digital output from the A/D converter22, demodulate a signal from a predetermined channel, and provide thedemodulated signal to the audio output circuit. In this case, the FFTarithmetic circuit 24 and the demodulation circuit 28 can be realized bya single DSP (Digital Signal Processor). However, the present inventionis not limited thereto, and as shown in FIG. 5, instead of thedemodulation circuit 28, there may be provided an analog demodulationcircuit 32 for receiving an analog output of the wideband filter 20 anddemodulating a selected predetermined channel.

Also in the above embodiment, the wideband filter 20 has a bandwidth of300 kHz, but the bandwidth is not limited thereto, and may be properlyset, considering nyquist interval, the number of samples to becalculated by the FFT arithmetic circuit 24 or the like. Alternatively,if it is possible, a wideband filter, which allows to pass through thesearch frequency range, may be arranged. In this case, the searchfrequency range itself may be designated as the scanning band, and inFIG. 3, it becomes possible to detect a channel in the search frequencyrange, without changing the local oscillation signal by the frequencysynthesizer.

Needless to say, the sampling frequency in the A/D converter 22 is notlimited to the one described in the above embodiment, and at least twicethe size of the bandwidth of non-sampling signals is sufficient. Forexample, if a signal input to the A/D converter is 10.7 MHz±150 kHz, itis only necessary that the sampling frequency of at least twice the sizeof the bandwidth, that is, 600 kHz or higher, and the frequency propertyof not lower than 10.7 MHz are ensured.

Moreover, in the above embodiment, as shown in FIG. 3, it is constructedsuch that when a channel is detected, in response to an instruction todemodulate the channel (step 306), a signal in a specified channel isdemodulated (step 307), and at the same time, other channels are scanned(step 304). As a result, while performing demodulation and output,detection of other channels can be performed, thereby enabling reductionin the processing time. However, the present invention is not limited tothe above processing. FIG. 7 shows another embodiment of the processing.In FIG. 7, the same processing steps as those in FIG. 3 are denoted bythe same numerals. As shown in FIG. 7, all the channels being incommunication are detected in the scanning band (step 704), andinformation regarding the channels is displayed on a screen of a displayunit, and the information is stored in a memory (step 705). When a userselects a certain channel, the demodulation circuit 28 demodulates thechannel and provides a signal to the audio output circuit. It is amatter of course that other processing forms may be taken.

In this embodiment, a signal demodulated by the demodulation circuit isprovided to the audio output circuit and the communication contents areoutput in speech. However, the construction is not limited thereto, andthe communication contents may be output to the display unit.

Moreover, in this specification, means do not always stand for aphysical means, and include a case where the function of each means isrealized by software. Furthermore, a function of one means may berealized by two or more physical means, or functions of two or moremeans may be realized by one physical means.

INDUSTRIAL APPLICABILITY

With the present invention, broadcasting, in which a predeterminedfrequency range is allocated for aeronautical radio and digital cellularphones, including narrow FM, commercial FM broadcasting and TVbroadcasting, and a plurality of channels are allocated in the allocatedfrequency range, that is, frequency band in a certain step, is scannedto detect a channel being in communication, and the contents can beoutput. Therefore, the present invention is applicable to the receiversand transmitters.

What is claimed is:
 1. A wideband receiver that receives radio wave, anduses a frequency range allocated to certain broadcasting as a searchfrequency range to detect a channel being in communication in saidsearch frequency range, comprising: a frequency converter which convertsthe frequency of a signal input via an antenna, by use of a localoscillation signal from a local oscillator; a wideband filter connectedto said frequency converter, which receives the output of said frequencyconverter to allow a signal component corresponding to a scanning bandincluding a bandwidth of at least a plurality of channels to passtherethrough; an A/D converter connected to said wideband filter, whichreceives said signal component and converts the signal component to adigital signal; an FFT arithmetic circuit connected to said A/Dconverter, which receives said digital signal and subjects the signal toa fast Fourier transform; a detection circuit which sequentially detectsone or more channels being in communication in a predetermined scanningband, based on the calculation result by means of said FFT arithmeticcircuit, and outputting the detection results; a demodulation circuitwhich demodulates and outputs a signal in a predetermined channel beingin communication; and a control circuit which specifies a channel beingin communication sequentially detected by said detection circuit,according to a predetermined instruction, and allows the demodulationcircuit to demodulate a signal in the specified channel; wherein saidreceiver is constructed such that while said demodulation circuitdemodulates and outputs a signal in the specified channel, saiddetection circuit operates for the detection of the remaining channels,in parallel with the demodulation by means of said demodulation circuit,and a frequency of said local oscillation signal is changed to changesaid scanning band, whereby a channel being in communication is detectedin an allocated frequency range.
 2. A wideband receiver according toclaim 1, wherein the width of the scanning band of said wideband filteris set to be: I _(bw) /C _(bw) >T _(fft) /T _(ch)+1 (wherein I_(bw) is ascanning band width, C_(bw) is a search frequency range, T_(fft) is timefor operation in the FFT arithmetic circuit, and T_(ch) is frequencycontrol time of a local oscillator).
 3. A wideband receiver according toclaim 1 or 2, wherein said demodulation circuit is connected to said A/Dconverter, and receives said digital signal to demodulate a signal inthe detected channel, so that demodulation by means of the demodulationcircuit is realized in parallel with the detection of the channel.
 4. Awideband receiver according to claim 1 or 2, wherein said demodulationcircuit is connected to said wideband filter, and receives the outputfrom said wideband filter to demodulate a signal in a predeterminedchannel, so that demodulation by means of the demodulation circuit isrealized in parallel with the detection of the channel.
 5. A wide bandreceiver that receives radio wave, and uses a frequency range allocatedto certain broadcasting as a search frequency range to detect a channelbeing in communication in said search frequency range, comprising:signal extraction means for extracting a signal corresponding to ascanning band corresponding to a search frequency range, or a scanningband obtained by dividing the search frequency range into at least two;power calculation means for receiving a signal extracted by said signalextraction means and calculating a power with respect to the frequency;channel detection means for sequentially detecting one or more channelsbeing in communication in the scanning band, based on the calculationresult from said power calculation means; a demodulation circuit fordemodulating and outputting a signal of a predetermined channel being incommunication; and a control circuit for specifying a channel being incommunication sequentially detected by said detection circuit, accordingto a predetermined instruction, and allowing the demodulation circuit todemodulate a signal in the specified channel; wherein the receiver isconstructed such that while said demodulation circuit demodulates andoutputs a signal in the specified channel, said detection circuitoperates for the detection of the remaining channels, in parallel withthe demodulation by means of said demodulation circuit, and a channelbeing in communication is detected in the search frequency range bychanging said scanning band according to need.
 6. A channel scanningmethod for receiving radio wave, using a frequency range allocated tocertain broadcasting as a search frequency range to detect a channelbeing in communication in said search frequency range, and demodulatingand outputting a signal in a predetermined channel, which is constructedto perform steps of: converting the frequency of a signal input via anantenna, by a local oscillation signal from a local oscillator; allowinga signal component corresponding to a scanning band including abandwidth of at least a plurality of channels to pass, amongintermediate frequency signals obtained by the frequency conversion;calculating a power with respect to the frequency of said signalcomponent; sequentially detecting one or more channels being incommunication in said scanning band, based on the power obtained by saidcalculation; specifying the sequentially detected channel being incommunication in accordance with a predetermined instruction; detectingremaining channels being in communication in parallel with demodulationand output of a signal in said specified channel; and repeatingconversion of the frequency of said local oscillation signal andchanging the scanning band, to detect channels being in communication inthe frequency range, and demodulating and outputting a signal in thespecified channel.
 7. A method according to claim 6, wherein the widthof the scanning band of said wideband filter is set to be: I _(bw) /C_(bw) >T _(fft) /T _(ch)+1 (wherein I_(bw) is a scanning band width,C_(bw) is a search frequency range, T_(fft) is time for operation in theFFT arithmetic circuit, and T_(ch) is frequency control time of a localoscillator).
 8. A channel scanning method for receiving radio wave,using a frequency range allocated to certain broadcasting as a searchfrequency range to detect a channel being in communication in saidsearch frequency range, and demodulating and outputting a signal in apredetermined channel, comprising steps of: converting the frequency ofa signal input via an antenna, by a local oscillation signal from alocal oscillator; obtaining a scanning range by dividing a searchfrequency range into at least two, when necessary; extracting a signalcorresponding to the scanning band; calculating a power of the extractedsignal with respect to the frequency; sequentially detecting one or morechannels being in communication in said scanning band, based on thecalculated power; specifying the sequentially detected channel being incommunication in accordance with a predetermined instruction; detectingremaining channels being in communication in parallel with demodulationand output of a signal in said specified channel; and repeatingconversion of the frequency of said local oscillation signal andchanging the scanning band, to detect channels being in communication inthe frequency range, and demodulating and outputting a signal in thespecified channel.